linux/tools/testing/radix-tree/iteration_check.c

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radix-tree tests: add iteration test There are four cases I can see where we could end up with a NULL 'slot' in radix_tree_next_slot(). This unit test exercises all four of them, making sure that if in the future we have an unsafe path through radix_tree_next_slot(), we'll catch it. Here are details on the four cases: 1) radix_tree_iter_retry() via a non-tagged iteration like radix_tree_for_each_slot(). In this case we currently aren't seeing a bug because radix_tree_iter_retry() sets iter->next_index = iter->index; which means that in in the else case in radix_tree_next_slot(), 'count' is zero, so we skip over the while() loop and effectively just return NULL without ever dereferencing 'slot'. 2) radix_tree_iter_retry() via tagged iteration like radix_tree_for_each_tagged(). This case was giving us NULL pointer dereferences in testing, and was fixed with this commit: commit 3cb9185c6730 ("radix-tree: fix radix_tree_iter_retry() for tagged iterators.") This fix doesn't explicitly check for 'slot' being NULL, though, it works around the NULL pointer dereference by instead zeroing iter->tags in radix_tree_iter_retry(), which makes us bail out of the if() case in radix_tree_next_slot() before we dereference 'slot'. 3) radix_tree_iter_next() via via a non-tagged iteration like radix_tree_for_each_slot(). This currently happens in shmem_tag_pins() and shmem_partial_swap_usage(). As with non-tagged iteration, 'count' in the else case of radix_tree_next_slot() is zero, so we skip over the while() loop and effectively just return NULL without ever dereferencing 'slot'. 4) radix_tree_iter_next() via tagged iteration like radix_tree_for_each_tagged(). This happens in shmem_wait_for_pins(). radix_tree_iter_next() zeros out iter->tags, so we end up exiting radix_tree_next_slot() here: if (flags & RADIX_TREE_ITER_TAGGED) { void *canon = slot; iter->tags >>= 1; if (unlikely(!iter->tags)) return NULL; Link: http://lkml.kernel.org/r/20160815194237.25967-3-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Shuah Khan <shuahkh@osg.samsung.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-10-12 04:51:21 +08:00
/*
* iteration_check.c: test races having to do with radix tree iteration
* Copyright (c) 2016 Intel Corporation
* Author: Ross Zwisler <ross.zwisler@linux.intel.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*/
#include <linux/radix-tree.h>
#include <pthread.h>
#include "test.h"
#define NUM_THREADS 4
#define TAG 0
static pthread_mutex_t tree_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_t threads[NUM_THREADS];
RADIX_TREE(tree, GFP_KERNEL);
bool test_complete;
/* relentlessly fill the tree with tagged entries */
static void *add_entries_fn(void *arg)
{
int pgoff;
while (!test_complete) {
for (pgoff = 0; pgoff < 100; pgoff++) {
pthread_mutex_lock(&tree_lock);
if (item_insert(&tree, pgoff) == 0)
item_tag_set(&tree, pgoff, TAG);
pthread_mutex_unlock(&tree_lock);
}
}
return NULL;
}
/*
* Iterate over the tagged entries, doing a radix_tree_iter_retry() as we find
* things that have been removed and randomly resetting our iteration to the
* next chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
* radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *tagged_iteration_fn(void *arg)
{
struct radix_tree_iter iter;
void **slot;
while (!test_complete) {
rcu_read_lock();
radix_tree_for_each_tagged(slot, &tree, &iter, 0, TAG) {
void *entry;
int i;
/* busy wait to let removals happen */
for (i = 0; i < 1000000; i++)
;
entry = radix_tree_deref_slot(slot);
if (unlikely(!entry))
continue;
if (radix_tree_deref_retry(entry)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
if (rand() % 50 == 0)
slot = radix_tree_iter_next(&iter);
}
rcu_read_unlock();
}
return NULL;
}
/*
* Iterate over the entries, doing a radix_tree_iter_retry() as we find things
* that have been removed and randomly resetting our iteration to the next
* chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
* radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *untagged_iteration_fn(void *arg)
{
struct radix_tree_iter iter;
void **slot;
while (!test_complete) {
rcu_read_lock();
radix_tree_for_each_slot(slot, &tree, &iter, 0) {
void *entry;
int i;
/* busy wait to let removals happen */
for (i = 0; i < 1000000; i++)
;
entry = radix_tree_deref_slot(slot);
if (unlikely(!entry))
continue;
if (radix_tree_deref_retry(entry)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
if (rand() % 50 == 0)
slot = radix_tree_iter_next(&iter);
}
rcu_read_unlock();
}
return NULL;
}
/*
* Randomly remove entries to help induce radix_tree_iter_retry() calls in the
* two iteration functions.
*/
static void *remove_entries_fn(void *arg)
{
while (!test_complete) {
int pgoff;
pgoff = rand() % 100;
pthread_mutex_lock(&tree_lock);
item_delete(&tree, pgoff);
pthread_mutex_unlock(&tree_lock);
}
return NULL;
}
/* This is a unit test for a bug found by the syzkaller tester */
void iteration_test(void)
{
int i;
printf("Running iteration tests for 10 seconds\n");
srand(time(0));
test_complete = false;
if (pthread_create(&threads[0], NULL, tagged_iteration_fn, NULL)) {
perror("pthread_create");
exit(1);
}
if (pthread_create(&threads[1], NULL, untagged_iteration_fn, NULL)) {
perror("pthread_create");
exit(1);
}
if (pthread_create(&threads[2], NULL, add_entries_fn, NULL)) {
perror("pthread_create");
exit(1);
}
if (pthread_create(&threads[3], NULL, remove_entries_fn, NULL)) {
perror("pthread_create");
exit(1);
}
sleep(10);
test_complete = true;
for (i = 0; i < NUM_THREADS; i++) {
if (pthread_join(threads[i], NULL)) {
perror("pthread_join");
exit(1);
}
}
item_kill_tree(&tree);
}